如何制作透明画布而不出错？

Question

I'm trying to get the background of a html5-starfield transparent.But why error?

This with background color black http://www.thediscopalace.com/testing.php

And this if background transparent http://www.thediscopalace.com/testing1.php

I change context.fillStyle='rgb(36,14,118)'; = BLACK to context.fillStyle='rgba(36,14,118, 0)'; = TRANSPARENT

Answer 1

The problem is in fact, that actually you're not cleaning the canvas before drawing new stars state. So you just need to change context.fillRect(0,0,w,h) inside anim() function to context.clearRect(0,0,w,h) .

It was working initially, because canvas was filled with opaque color each time new stars state were drawn, but after your changes that color become transparent.